VDR is expressed in most immune cells, including B- and T-lymphocytes, monocytes, macrophages, and DCs, and some of these are able to convert 25-hydroxy vitamin D to 1,25 (OH)2D. For example, in the presence of infection, activated macrophages and monocytes, induced by TLR signaling and inflammatory cytokines, express CYP27B1 which converts 25(OH)D into 1,25(OH)2D. 1,25(OH)2D then enhances macrophages and monocyte antimicrobial activity by stimulating their production of endogenous cathelicidin via VDR signaling (108–110). Here, CYP27B1 is linked to infection.